Lib.sol

pragma solidity ^0.5.0;

library simpleCalculator  {
    
    event actionHappened(string action, uint result);
    
    function addition(uint a, uint b) public{
        emit actionHappened("addition", a+b);
    }
    
    function deduction(uint a, uint b) public {
        emit actionHappened("deduction", a-b);
    }
    
    function multiply(uint a, uint b) public {
        emit actionHappened("multiply", a*b);
    }
    
    function division(uint a, uint b) public {
        emit actionHappened("division", a/b);
    }
    
    
}

contract Calculator {
    
    // using simpleCalculator for string;
    using simpleCalculator for uint;
    
    function add(uint a, uint b) public  {
        return a.addition(b);
    }
    
    function subtract(uint a, uint b) public {
        require(a>b || a==b, "not working like this");
        return a.deduction(b);
    }
}

contract Calculator2 {
    using simpleCalculator for uint;
    
    function multiply(uint a, uint b) public {
        return a.multiply(b);
    }
    
    function divide(uint a, uint b) public {
        a.division(b);
    }
}