Please do not use "..." when defining notations. Ellipses are helpful for giving a visual demonstration of how an expression expands, but they are often unclear or ambiguous, especially for complex recursion as seen in array notations. For beginners, I recommend that the "..." symbol not be used at all except in examples.

Use recursion instead. Instead of writing

{a,b,c+1} = a {c} a {c} ... (b times) ... {c} a {c} a

you should write

{a,1,c} = a
{a,b+1,c+1} = {a,{a,b,c+1},c}.