Turing machine that goes left on first symbol

Question

I have a turing machine with transitions given by the following table

I'm inputting the string aaaa. So if I look at the first symbol "a" in state A, it says to replace it with an X, go into state B, and move Left. This is where I'm confused. How can I move left if I'm looking at the first input symbol? Do I just go to a blank symbol?

Thanks!

Answer 1

Turing machine tapes are usually taken to be infinite in both directions, so the machine starts looking at the first input symbol, but there's an infinite supply of blanks to the left of that.