My `~/.XCompose` file. Modified from the Fabien's version.

.XCompose

#|
#| File    : ~/.XCompose
#| Author  : Fabien Cazenave
#| Source  : https://github.com/fabi1cazenave/dotFiles
#| Licence : WTFPL
#|

include "/usr/share/X11/locale/en_US.UTF-8/Compose"

# These files are worth checking for more ~/.XCompose madness:
# https://github.com/kragen/xcompose
# http://ootync-xcompose.googlecode.com/files/.XCompose
# https://github.com/luispedro/base-user/blob/master/configuration-files/XCompose

# arrows

<Multi_key> <h> <h>   : "←" U2190 # LEFTWARDS ARROW
<Multi_key> <k> <k>   : "↑" U2191 # UPWARDS ARROW
<Multi_key> <l> <l>   : "→" U2192 # RIGHTWARDS ARROW
<Multi_key> <j> <j>   : "↓" U2193 # DOWNWARDS ARROW
<Multi_key> <H> <H>   : "⇐" U21D0 # LEFTWARDS DOUBLE ARROW
<Multi_key> <K> <K>   : "⇑" U21D1 # UPWARDS DOUBLE ARROW
<Multi_key> <L> <L>   : "⇒" U21D2 # RIGHTWARDS DOUBLE ARROW
<Multi_key> <J> <J>   : "⇓" U21D3 # DOWNWARDS DOUBLE ARROW

<Multi_key> <h> <l>   : "↔" U2194 # LEFT RIGHT ARROW
<Multi_key> <l> <h>   : "↔" U2194 # LEFT RIGHT ARROW
<Multi_key> <j> <k>   : "↕" U2195 # UP DOWN ARROW
<Multi_key> <k> <j>   : "↕" U2195 # UP DOWN ARROW
<Multi_key> <H> <L>   : "⇔" U21D4 # LEFT RIGHT DOUBLE ARROW
<Multi_key> <L> <H>   : "⇔" U21D4 # LEFT RIGHT DOUBLE ARROW
<Multi_key> <J> <K>   : "⇕" U21D5 # UP DOWN DOUBLE ARROW
<Multi_key> <K> <J>   : "⇕" U21D5 # UP DOWN DOUBLE ARROW

# common symbols

<Multi_key> <equal> <v>             : "✓" U2713 # CHECK MARK
<Multi_key> <equal> <V>             : "✔" U2714 # HEAVY CHECK MARK
<Multi_key> <equal> <x>             : "✗" U2717 # BALLOT X
<Multi_key> <equal> <X>             : "✘" U2718 # HEAVY BALLOT X
<Multi_key> <equal> <space> <space> : "☐" U2610 # BALLOT BOX
<Multi_key> <equal> <space> <v>     : "☑" U2611 # BALLOT BOX WITH CHECK
<Multi_key> <equal> <space> <x>     : "☒" U2612 # BALLOT BOX WITH X

<Multi_key> <equal> <dot>           : "•" U2022 # BULLET
<Multi_key> <equal> <greater>       : "‣" U2023 # TRIANGULAR BULLET
<Multi_key> <equal> <asterisk>      : "★" U2605 # BLACK STAR

<Multi_key> <o> <percent>           : "‰" U2030 # PER MILLE SIGN
<Multi_key> <o> <x>                 : "¤" U00A4 # CURRENCY SIGN
<Multi_key> <o> <o>                 : "°" U00B0 # DEGREE SIGN
<Multi_key> <o> <C>                 : "℃" U2103 # DEGREE CELSIUS
<Multi_key> <o> <F>                 : "℉" U2109 # DEGREE FARENHEIT

# superscript

<Multi_key> <k> <0>            : "⁰"
<Multi_key> <k> <1>            : "¹"
<Multi_key> <k> <2>            : "²"
<Multi_key> <k> <3>            : "³"
<Multi_key> <k> <4>            : "⁴"
<Multi_key> <k> <5>            : "⁵"
<Multi_key> <k> <6>            : "⁶"
<Multi_key> <k> <7>            : "⁷"
<Multi_key> <k> <8>            : "⁸"
<Multi_key> <k> <9>            : "⁹"

<Multi_key> <k> <plus>         : "⁺"
<Multi_key> <k> <minus>        : "⁻"
<Multi_key> <k> <equal>        : "⁼"
<Multi_key> <n> <equal>        : "≠"
<Multi_key> <k> <parenleft>    : "⁽"
<Multi_key> <k> <parenright>   : "⁾"
<Multi_key> <k> <i>            : "ⁱ"
<Multi_key> <k> <n>            : "ⁿ"

# subscript

<Multi_key> <j> <0>            : "₀"
<Multi_key> <j> <1>            : "₁"
<Multi_key> <j> <2>            : "₂"
<Multi_key> <j> <3>            : "₃"
<Multi_key> <j> <4>            : "₄"
<Multi_key> <j> <5>            : "₅"
<Multi_key> <j> <6>            : "₆"
<Multi_key> <j> <7>            : "₇"
<Multi_key> <j> <8>            : "₈"
<Multi_key> <j> <9>            : "₉"

<Multi_key> <j> <plus>         : "₊"
<Multi_key> <j> <minus>        : "₋"
<Multi_key> <j> <equal>        : "₌"
<Multi_key> <j> <parenleft>    : "₍"
<Multi_key> <j> <parenright>   : "₎"
<Multi_key> <j> <i>            : "ᵢ"
#<Multi_key> <j> <n>           (N/A)

# emoticons

<Multi_key> <comma> <l>            : "♡" U2661 # WHITE HEART SUIT
<Multi_key> <comma> <L>            : "♥" U2665 # BLACK HEART SUIT
<Multi_key> <comma> <3>            : "♥" U2665 # BLACK HEART SUIT

<Multi_key> <dot> <2>              : "☹" U2639 # WHITE FROWNING FACE
<Multi_key> <dot> <parenleft>      : "☹" U2639 # WHITE FROWNING FACE
<Multi_key> <dot> <3>              : "☺" U263A # WHITE SMILING FACE
<Multi_key> <dot> <parenright>     : "☺" U263A # WHITE SMILING FACE

<Multi_key> <dot> <d>              : "😃" U1F603 # SMILING FACE WITH OPEN MOUTH
<Multi_key> <dot> <D>              : "😃" U1F603 # SMILING FACE WITH OPEN MOUTH
<Multi_key> <o> <dot> <3>          : "😇" U1F607 # SMILING FACE WITH HALO
<Multi_key> <o> <dot> <parenright> : "😇" U1F607 # SMILING FACE WITH HALO
<Multi_key> <comma> <3>            : "😉" U1F609 # WINKING FACE
<Multi_key> <comma> <parenright>   : "😉" U1F609 # WINKING FACE
<Multi_key> <dot> <p>              : "😋" U1F60B # FACE SAVOURING DELICIOUS FOOD
<Multi_key> <dot> <P>              : "😋" U1F60B # FACE SAVOURING DELICIOUS FOOD
<Multi_key> <B> <3>                : "😎" U1F60E # SMILING FACE WITH SUNGLASSES
<Multi_key> <B> <parenright>       : "😎" U1F60E # SMILING FACE WITH SUNGLASSES



##############################################################
###### SECTION-2 #############################################
###### Source: https://gist.github.com/pkgw/5422749 ##########
##############################################################

# PKGW customizations
# Greek ambiguities: epsilon/eta, theta/tau, pi/phi/psi, omega/omicron

<Multi_key> <backslash> <comma> : " " U202F # thin nonbreaking space

<Multi_key> <g> <a> : "α"
<Multi_key> <g> <b> : "β"
<Multi_key> <g> <g> : "γ"
<Multi_key> <g> <d> : "δ"
<Multi_key> <g> <3> : "ε" # note! 
<Multi_key> <g> <z> : "ζ"
<Multi_key> <g> <e> : "η"
<Multi_key> <g> <h> : "θ" # note!
<Multi_key> <g> <i> : "ι"
<Multi_key> <g> <k> : "κ"
<Multi_key> <g> <l> : "λ"
<Multi_key> <g> <m> : "μ"
<Multi_key> <g> <n> : "ν"
<Multi_key> <g> <x> : "ξ"
# note: no omicron
<Multi_key> <g> <p> : "π"
<Multi_key> <g> <r> : "ρ"
<Multi_key> <g> <s> : "σ"
<Multi_key> <g> <t> : "τ"
<Multi_key> <g> <u> : "ψ"
<Multi_key> <g> <f> : "φ" # note!
<Multi_key> <g> <c> : "χ"
<Multi_key> <g> <o> : "ω"

<Multi_key> <g> <G> : "Γ"
<Multi_key> <g> <D> : "Δ"
<Multi_key> <g> <H> : "Θ"
<Multi_key> <g> <L> : "Λ"
<Multi_key> <g> <X> : "Ξ"
<Multi_key> <g> <P> : "Π"
<Multi_key> <g> <S> : "Σ"
<Multi_key> <g> <F> : "Φ"
<Multi_key> <g> <U> : "Ψ"
<Multi_key> <g> <O> : "Ω"

<Multi_key> <B> <A> : "𝔸"
<Multi_key> <B> <B> : "𝔹"
<Multi_key> <B> <C> : "ℂ"
<Multi_key> <B> <D> : "𝔻"
<Multi_key> <B> <E> : "𝔼"
<Multi_key> <B> <F> : "𝔽"
<Multi_key> <B> <G> : "𝔾"
<Multi_key> <B> <H> : "ℍ"
<Multi_key> <B> <I> : "𝕀"
<Multi_key> <B> <J> : "𝕁"
<Multi_key> <B> <K> : "𝕂"
<Multi_key> <B> <L> : "𝕃"
<Multi_key> <B> <M> : "𝕄"
<Multi_key> <B> <N> : "ℕ"
<Multi_key> <B> <O> : "𝕆"
<Multi_key> <B> <P> : "ℙ"
<Multi_key> <B> <Q> : "ℚ"
<Multi_key> <B> <R> : "ℝ"
<Multi_key> <B> <S> : "𝕊"
<Multi_key> <B> <T> : "𝕋"
<Multi_key> <B> <U> : "𝕌"
<Multi_key> <B> <V> : "𝕍"
<Multi_key> <B> <W> : "𝕎"
<Multi_key> <B> <X> : "𝕏"
<Multi_key> <B> <Y> : "𝕐"
<Multi_key> <B> <Z> : "ℤ"


<Multi_key> <r> <r> : "₹"