Now consider a propositional function Fx in which the variable argument x is itself a propositional function.
Call it a propositional function; and, if 4)x be a propositional function, the undetermined variable x is the argument.
A similar theory holds for relations which arise from the consideration of propositional functions with two or more variable arguments.
The road to hell: intentions & propositional attitude ascription.
The satisfiability problem for the propositional calculus; Cook's theorem.