```pragma solidity ^0.4.7;
/**
@dev Math operations with safety checks that throw on error
/
library SafeMath {
function mul(uint256 a, uint256 b) internal constant returns (uint256) {
uint256 c = a b;
assert(a == 0 || c / a == b);
return c;
}
function div(uint256 a, uint256 b) internal constant returns (uint256) {
// assert(b > 0); // Solidity automatically throws when dividing by 0
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}
function sub(uint256 a, uint256 b) internal constant returns (uint256) {
assert(b <= a);
return a - b;
}
function add(uint256 a, uint256 b) internal constant returns (uint256) {
uint256 c = a + b;
assert(c >= a);
return c;
}
}
11 browser/Untitled.sol:11:5: Error: Undeclared identifier.
assert(a == 0 || c / a == b);
^----^
23 browser/Untitled.sol:23:5: Error: Undeclared identifier.
assert(b <= a);
^----^
29 browser/Untitled.sol:29:5: Error: Undeclared identifier.
assert(c >= a);
^----^
string storage description;
and see if that helps.