SafeMath.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.4 <0.7.0;
pragma experimental ABIEncoderV2;


// Implementacion de la libreria SafeMath para realizar las operaciones de manera segura
// Fuente: "https://gist.github.com/giladHaimov/8e81dbde10c9aeff69a1d683ed6870be"

library SafeMath{
    // Restas
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
      assert(b <= a);
      return a - b;
    }
    
    // Sumas
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
      uint256 c = a + b;
      assert(c >= a);
      return c;
    }
    
    // Multiplicacion
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }
}