.PS
cct_init

   up_
Q1: bi_tr(up_ dimen_) 
   thinlines_
   box dotted ht last [].ht wid last [].wid at last []
   thicklines_
   "\hbox{\sl E}" at Q1.E-(0,0.05) below    
   "\hbox{\sl B}sp_" at Q1.B rjust    
   "\hbox{\sl C}" at Q1.C above    
   "{\tt bi\_tr(up\_ dimen\_)}" at Q1.s + (0,-0.2) below

Q2: bi_tr(,R) with .E at Q1.E+(0.75,0) 
   thinlines_
   box dotted ht last [].ht wid last [].wid at last []
   thicklines_
   "\hbox{\sl E}" at Q2.E-(0,0.05) below    
   "sp_\hbox{\sl B}" at Q2.B ljust    
   "\hbox{\sl C}" at Q2.C above    
   "{\tt bi\_tr(,R)}" at Q2.s + (0,-0.2) below

Q3: bi_tr(,,P) with .C at Q2.C+(1.25,0) 
   thinlines_
   box dotted ht last [].ht wid last [].wid at last []
   thicklines_
   "\hbox{\sl E}" at Q3.E-(0,0.05) below    
   "\hbox{\sl B}sp_" at Q3.B rjust    
   "\hbox{\sl C}" at Q3.C above    
   "{\tt bi\_tr(,,P)}" at Q3.s + (0,-0.2) below

Q4: bi_tr(,,,E) with .C at Q3.C+(1,0) 
   thinlines_
   box dotted ht last [].ht wid last [].wid at last []
   thicklines_
   "\hbox{\sl E}" at Q4.E-(0,0.05) below    
   "\hbox{\sl B}sp_" at Q4.B rjust    
   "\hbox{\sl C}" at Q4.C above    
   "{\tt bi\_tr(,,,E)}" at Q4.s + (0,-0.2) below

.PE