Theorem fimass

Description: The image of a class under a function with domain and codomain is a subset of its codomain. (Contributed by Glauco Siliprandi, 17-Aug-2020)

	Ref	Expression
Assertion	fimass	|- ( F : A --> B -> ( F " X ) C_ B )

Proof

Step	Hyp	Ref	Expression
1		imassrn	|- ( F " X ) C_ ran F
2		frn	|- ( F : A --> B -> ran F C_ B )
3	1 2	sstrid	|- ( F : A --> B -> ( F " X ) C_ B )