Complex sentence: This axiomatic theory did not allow the construction of the ordinal numbers; while most of "ordinary mathematics" can be developed without ever using ordinals, ordinals are an essential tool in most set-theoretic investigations.
Split into simpler sentences: This axiomatic theory did not allow the construction of the ordinal numbers. While most of "ordinary mathematics" can be developed without ever using ordinals, ordinals are an essential tool in most set-theoretic investigations.