problem: !SequentialCoupling
  primary_equation: !Unsteady_LMH
    input_fields:
      - region: .left
        bc_type: neumann
        bc_flux: !FieldElementwise
            file: xyz.msh
            
      - region: .right
        bc_type: total_flux
        bc_flux: !FieldInterpolatedP0
            file: xyz.msh
            
  secondary_equation: !SoluteTransport_DG
    input_fields:
      - region: .left
        bc_type: robin
        bc_flux: !FieldPython
            file: xyz.py
