Question

Show that one cannot infer from the formula ∃xR0(x,c) the formula ∃xR0(c,x)

Answer 1

I'm looking for help to understand the difference of these formulas

Answer 2

that's just been asked on stackexchange, so when someone solves this post it there too.
http://math.stackexchange.com/questions/356970/show-that-one-cannot-infer-from-the-formula-xr0x-c-the-formula-xr0c-x
or if they solve it first, just go there.

Answer 3

where is the problem from?

Answer 4

yes I asked it in stackexchange.... The problem is from my logic 1 course. Maybe I don't understand what does it matter if it's (c,x) or (x,c) in a binary relation (if that is what R typically denotes..)

Answer 5

so (c,x) would mean "the constant c's relation to (variable) x" and (x,c) would mean "the variable x's relation to constant c"?

Answer 6

well a simple relation could be x is related to y if x is the parent of y. so john R arnold becuase john is the parent of arnold. but the converse is false.