Are the following relationships a function?

R = {-2, 5}, {3, 5}, {6, 4}

S = {4, 5}, {6, 7}, {4, 5}

T = {9, 0}, {8, 7}, {9, -4}

R is a function.

S is a function.

T is not a function because 9 goes to two distinctive values, which are 0 and 4.

Is my reasoning correct?