An exercise problem once again has me stumped on a Turing Machine decidability proof.
We are given an alphabet with the strings 0 through 9.
Along with this, we have x as the infinite string of all digits in PI. (3141592...)
With L ⊆ Σ*, the language L = {A ∈ Σ*| A is a sub-sequence of x}. (from what I understand, the definition here of a sub-sequence is having a $x = x_1x_2x_3... $ where each $x_i$ can be constructed from Σ, then a sub-sequence of x is a finite string of the form $x_{i1}x_{i2}x_{i3} ... x_{ik}$ where $i_1 < i_2 < i_3 < ... < i_k.$
Other than that I have no idea where to start with this...
Thanks in advance.