List all the elements of x that are less than 30 - the set

Question

Define a set X of numbers as follows.

B. 2 ∈ X.

R₁. If x ∈ X, so is 10x.

R₂* If x ∈ X, so is x + 4.

List all the elements of X that are less than 30.

The set X of all binary strings (strings with only O's and 1's) having the same number of O's and 1's is defined as follows.

B. λ is in X.

R₁. If x is in X, so are 1x0 and Ox1.

R₂. If x and y are in X, so is xy.

B. ________is in Y.

R₁. If y is in Y, so are _____________ and yx for any 

R₂ If y and y are in Y so is ___________

Give a recursive definition for the set Y of all binary strings with more O's than 1's.