Question: simplify/assuming

1. Why doesn't simplify(subs(...)) as a single expression work?

simplify(subs(z = -z, erf(z)));
subs(z = -z, erf(z));
simplify(%);
                           erf(-z)
                           erf(-z)
                           -erf(z)

2. This just hangs. Would be nice if simplify could deal with this, but in any case I don't think it should take so long:

timelimit(60, simplify(n <= p*n+sqrt(n)*p*(1-p))) assuming n > p*(n+(1-p)*sqrt(n));
Error, (in assuming) when calling '`property/ObjProperty`'. Received: 'time expired'

3. It seems that assuming doesn't like f(constant) objects. Doesn't seem right, because x(a) would work fine:

simplify(abs(x(0))) assuming x(0) > 0;
                          abs(x(0))

simplify(abs(y)) assuming x(0) > 0, y > 0;
Error, (in assuming) when calling 'assume'. Received: 'cannot assume on a constant object'

4. Can simplify be made to work on things like this (since it can handle the coefficient at (t+1))?

simplify((sqrt(1-I)*sqrt(1+I)-sqrt(2))*(t+1));
               -(-sqrt(1-I)*sqrt(1+I)+sqrt(2))*(t+1)