εἰμί to be versus εἶμι I'll go

 
εἶμι (to go) has a stem iota (real or subscript) in ALL of its forms,
but no stem sigma

 

Infinitive
to be to go
εἶναι ἰέναι
Compounds
Note that he accent is not recessive in Infinitives
to be present 
to be absent 
to be/live together  
παρεῖναι
ἀπεῖναι
συνεῖναι
παριέναι
απιέναι
συνιέναι
προσιέναι
ἐπανιέναι
to go past   
to go away 
to go together; meet  
to go up to 
to go back 

 

Participle
being going
ὤν
οὖσα
ὄν
ών
οῦσα
όν
  Only difference: going has a stem iota,
  Only difference: being has not, in Greek that is!
  And remember that participles are  declined ,
masculine and neuter like 3rd declension nouns,
feminine like 1st declension nouns ending in short .
Compounds
Note that the accent is not recessive in participles either.
the present 
her being absent (acc) 
those being together  
τὸ παρόν
τὴν ἀποῦσαν
οἱ συνόντες
παριόν
τὴν ἀπιοῦσαν
οἱ συνιόντες
τῷ προσιόντι
τῶν ἐπανιόντων
it going past (the animal e.g.) 
her going away (acc) 
those meeting  
to him approaching (dat) 
of those going back 

 

Imperative
be! go!
 be! (sg)
 let him/her/ be!
 be! (pl)
 let them be!
ἴσθι
ἔστω
ἔστε
ἔστων/ὄντων  
ἴθι
ἴτω
ἴτε
ἰόντων  
 go! (sg)
 let him/her/it go
 go! (pl)
 let them go
Compounds
Note that he accent is recessive in imperatives
be present! 
let them be absent 
tbe/live together!  
πάρισθι
ἀπέστων/ἀπόντων
σύνεστε
πάριθι
ἀπιόντων  
σύνιτε
ἐπανίτω
go past! (sg.)   
let them go away! 
go together!  
let her go back!