feat(27): add text about cauchy sequences
feat(27): add text about cauchy sequences

leanprover/logic_and_proof,fpvandoorn/logic_and_proof,avigad/logic_and_proof,rlewis1988/logic_and_proof,fpvandoorn/logic_and_proof,leanprover/logic_and_proof,avigad/logic_and_proof,rlewis1988/logic_and_proof,fpvandoorn/logic_and_proof,avigad/logic_and_proof,leanprover/logic_and_proof,rlewis1988/logic_and_proof