Inspired by [this](https://twitter.com/robinhouston/status/1569302339508396033?s=20&t=jM-WoWc9Z9SfL1--xVhX8g) tweet, pairing of strings!

pairstrings.jl

"Pair"
function ↑(a::String, b::String)
    a * '0' * b * a * '1' * b
end

"""
Unpair one step
"""
function ↓(p::String)
    mid = length(p) ÷ 2    
    diff = findfirst(i -> p[i] != p[i + mid], 1:mid)

    if p[diff] ∉ ('0', '1') 
        return (p, "")
    end

    return (p[1:diff - 1], p[diff + 1:mid])
end

"Unpair recursively till bottom of tree"
function ⤈(p::String)
    p′, word = ↓(p)
    if p′ == p return p′ end

    return (⤈(p′), word)
end

encoded = ("Hello" ↑ "world") ↑ "!"
⤈(encoded) # (("Hello", "world"), "!")