Input tax definition differences restrict cross-utilisation of CGST and SGST credits while allowing all credits against IGST liability. Different statutory definitions of input tax mean CGST treats input tax as IGST and CGST, SGST treats it as IGST and SGST, and IGST treats it as IGST, CGST and SGST; consequently, all three credits can discharge IGST liability, but CGST liabilities may be met only with IGST and CGST credits and SGST liabilities only with IGST and SGST credits, preventing direct cross-utilisation of CGST and SGST credits.