If we have two functions: and .

When taking the convolution we replace t with let's say for , so we didn't change it.

The fun ends when for the other function we write . If we have on the abscissa now , so when we add the minus sign inside then we reflect the function across the .

Now we must move the function to the far left. So if I understand correctly we write instead of when integrated, because we move it to the left. Because if we have function then we move it to the in the left direction.

But what about ?