Indexed instructions
  LDA $23,x
    Accesses the memory x bytes past memory @ 23.
    Direct access with an indexed offset.

  LDA ($23),y
    EA = 2 byte address stored in memory 23 & 24 + content of y register.
    Memory based indirect with indexed offset.
    
  LDA ($23,x)
    EA =  2 byte address found x bytes past memory @ 23. (table of @)
    Memory based indirect with indexed offset. Index applied at different
    step of effective address evalulation. Index access a table of indirect
    pointers.