I'm self-studying discrete mathematics using the Rosen textbook, and I'm trying to get some predicate logic terms straight. Using definitions from that textbook:
The propositional function
"x < 3", and has as its subject the variable
x, and as its predicate
< 3. The predicate does not use the variable.
"x = y + z", what is its predicate?
It seem awkward to state the predicate without using the variables. (And not using them does not seem to serve any purpose, since they are only defined within the scope of the propositional function, and so I think they won't interfere with any other propositional functions.)
By analogy with English grammar, I suppose
Q(x,y,z) would be considered to have a subject that is a compound subject of the tuple
(x,y,z), but that doesn't help with the predicate.
I notice that some binary relational predicates can be stated as the words between the variables, such as
"is taller than" or
"is parent of", but this will not always work for every n-ary propositional function in general - such as
"x = y + z".
Perhaps I'm demanding too much precision in these terms - but precision is the reason I'm studying this, so I'd really like to know. :-) Thanks for any clarification/correction.