sign(cos(x)-1) => pnz (should be nz)
sign(max(x,1)) => pnz (should be pos)
It would be nice if COMPAR knew a few things about the
range of common functions, e.g. that -1 <= sin/cos(x)
<= 1, -%pi/2 < atan(x) < %pi/2, -%pi/2 <= asin(x) <= %
pi/2, 0<=acos(x)<=%pi, 1 <= cosh(x), -1 < tanh(x) < 1, -
1 <= signum(x) <= 1, etc.
It does know that 0< exp(x) and 0<=abs(x), for example -
- though this is special-cased, not table-driven. But it
should also know about max, min. And that entier(x) <=
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