Output of propositional functions

[Alberto Candel]

A propositional function outputs 0/1 or True/False depending on ...? Maybe someone knows how to always get True/False. I explain:

The function gt0(x):=x>0 outputs 0/1: for example gt0(2)=1 and gt0(-1)=0. But the function ge0(x):=x ≥ 0 outputs True/False (≥ is the html code for "at least"), for example ge0(2)=True and ge0(-3)=False.

Is there some kind of switch that will always give True/False as possible answers?

BTW, Xcas seems to always return True/False