Validation logic for internal lookup field

I’m trying to create display logic for a field based on the value of a single-select internal lookup field. Does anyone know the validation code I should use? I’ve tried all of these and nothing is working:

IF({DE:Lookup field}=”value1”, true)

IF({DE:Lookup field}.{name}=”value1”, true)

IF(CONTAINS(“value1”,{DE:Lookup field}), true)

IF(CONTAINS(“value1”,{DE:Lookup field}.{name}), true)

Thanks!