Recursion
From Tardis Wiki, the free Doctor Who reference
Recursion is a concept of ideas and concepts repeating within themselves, this concept, specially "if we had an index file we could look up index file in the index file" (or words to that effect) which gave Tegan Jovanka the idea to search the TARDIS index file using the letters IF. (DW: Castrovalva)Once, the Master tricked the Doctor into materializing his TARDIS around the Master's, creating a dimensionally recursive loop
