problem: !SequentialCoupling
  primary_equation: !Unsteady_LMH
    input_fields:
      - region: .left
        bc_type: neumann
      # Change sign of this field manually.
        COMMENTED_bc_flux: !FieldElementwise
          file: xyz.msh

      - region: .right
        bc_type: total_flux
      # Change sign of this field manually.
        COMMENTED_bc_flux: !FieldInterpolatedP0
          file: xyz.msh

  secondary_equation: !SoluteTransport_DG
    input_fields:
      - region: .left
        bc_type: robin
      # Change sign of this field manually.
        COMMENTED_bc_flux: !FieldPython
          file: xyz.py
