LRMQ
      +---------
LYPTU | UQRGNNFG
       -RPTMQ
        =====
         JYHYN
        -MTQRU
         =====
         NHPNJF
        -NWLRYX
         ======
          NQTUFG
         -NMMGGU
          ======
           NGLQP

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: challenging
hints: R << M