//To be used by the gui code in one assembly
class guiData : ICommonData
{
    // Implement ICommonData Members

    // Some data for guiData only
}

// GUI would implement this interface in order to access the solver
Interface ISolver
{
    IOutput RunTheSolver(ICommonData input)
}


//To be used by the solver code another assembly
class solverData : ICommonData
{
    // Implement ICommonData Members

    // Some data for solverData only
}


interface ICommonData
{
    //Data that must be transfered between the gui and the solver
}