plotting – Cannot understand meaning of “identical”

This came up in the context of plotting solutions to NDSolve, but I’ve reduced it to the following issue. This really has me scratching my head.

points = {{0, 0}, {1, 1}, {2, 3}, {3, 4}, {4, 3}, {5, 0}};
ifun = Interpolation[points]

ifun is now an InterpolatingFunction. I cannot plot ifun, but I can plot ifun


If I make the following assignment, I cannot plot ifun2


In other words, the following statement will not plot anything:


However, if I do this:

ifun3[t_] = ifun

I can plot ifun3


The answer is “True”. Similarly for ifun3