infix "and" (other: BOOLEAN): BOOLEAN 
         -- Boolean conjunction with `other'
   infix "and then" (other: BOOLEAN): BOOLEAN 
         -- Boolean semi strict conjunction with `other'
   infix "implies" (other: BOOLEAN): BOOLEAN
         -- Boolean implication of `other'
   infix "or" (other: BOOLEAN): BOOLEAN
         -- Boolean disjunction with `other'
   infix "or else" (other: BOOLEAN): BOOLEAN
         -- Boolean semi strict disjunction with `other'
   infix "xor" (other: BOOLEAN): BOOLEAN
         -- Boolean exclusive or with `other'