lookup for τέθνατε 2nd plural indicative, it produces no results
lookup for τεθναῖτον or τεθναίτην (dual), τεθναῖμεν , τεθναῖτε (optative poetic) it produces no results
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Finally I was able to find this verb on Smyth (I could not find any reference in the Greek index and the list of verbs, though). in Smyth section 417 there is a reference to this verb in section 704.c
there are fewer endings than in Mastronarde e.g. 2 perf dual τέθνατον but not mention to the 3rd person dual. Probably Morpheus does not have this ending as it is not in Smyth too like all the other endings reported above except for τέθνατε 2nd plural indicative which is listed in Smyth.
Either we remove some endings from the table to match Smyth and we 'fix' Morpheus for τέθνατε or we leave as is.
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Originally posted by @monzug in https://github.com/alpheios-project/alpheios-core/issues/63#issuecomment-587020574