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contract SafeMath {
function safeMul(uint256 a, uint256 b) internal returns (uint256) {
uint256 c = a * b;
assert(a == 0 || c / a == b);
return c;
}
function safeDiv(uint256 a, uint256 b) internal returns (uint256) {
assert(b > 0);
uint256 c = a / b;
assert(a == b * c + a % b);
return c;
}
function safeSub(uint256 a, uint256 b) internal returns (uint256) {
assert(b <= a);
return a - b;
}
function safeAdd(uint256 a, uint256 b) internal returns (uint256) {
uint256 c = a + b;
assert(c>=a && c>=b);
return c;
}
function assert(bool assertion) internal {
if (!assertion) {
throw;
}
}
}