See International Character Set Support, B035-1125 for the internal mappings that Vantage uses for the LOWER function.
Teradata SQL has the type attribute NOT CASESPECIFIC that allows case blind comparisons, but the type attributes CASESPECIFIC and NOT CASESPECIFIC are Teradata extensions to the ANSI standard.
For ANSI portability, use the UPPER function for case blind comparisons with ANSI-compliant syntax.