function of 2 variables in UML, how to define relation?

function of 2 variables in UML, how to define relation?

when we have a a Relation of 1 variable such as Y=R1(X)(i used closed-form
representation of my relation instead of tree or table representaton or )
with Xdomain={1,3,4},Ydomain={a,b},order pairs={(1,a),(1,b),(3,b),(4,b)},i
can depict 2 diagrams to show for each domain and connect pairs to
represent my relation.In UML, i can depict 2 classes and relate them by a
line. when Y is a function of 2 variables instead of 1 Y=R2(X,Z), I can't
change R2 relationship into a relationship of one variable and can't
depict it with 3 diagrams unless there is a relationship between X and Z
(X=R3(Z)) and in this case Y=R2(X,R3(X)).
>
with this hypothese that we have R3(),I can depict 3 diagrams and connect
them one-by one.In UML how can i show it by classes?do i use a dependency
relation R3 between classes X and Z, and an association relation R2(R3())
between classes X and Y?
I hope that the question is clear enough for you and thanks in advance