main script 1:
Break on
If Not IsDeclared($_UDF_LIB) Call @scriptdir+'\UDFs.kix' EndIf
...

Main script 2:
Break on
If Not IsDeclared($_UDF_LIB) Call @scriptdir+'\UDFs.kix' EndIf
...

UDF Script:
If Not IsDeclared($_UDF_LIB)
Global $_UDF_LIB
EndIf
...
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