extern bool divide(const ex &a, const ex &b, ex &q, bool check_args = true);
// Polynomial GCD in Z[X], cofactors are returned in ca and cb, if desired
-extern ex gcd(const ex &a, const ex &b, ex *ca = NULL, ex *cb = NULL,
- bool check_args = true, unsigned options = 0);
+extern ex gcd(const ex &a, const ex &b, ex *ca = nullptr, ex *cb = nullptr,
+ bool check_args = true, unsigned options = 0);
// Polynomial LCM in Z[X]
extern ex lcm(const ex &a, const ex &b, bool check_args = true);