Database Query Problem??

Hi i have got a database with the following tables below:

Patient (PatientCode, PatientSurname, PatientFirstname, PatientSex, Age, PatientOccupation, PatientHeight, PatientWeight, PatientAddress)

Doctor (DoctorCode, DoctorSurName, DoctorFirstName, DoctorPrivateAddress, MobileNo, Function)

Operation (Operation Code, PatientCode, DoctorCode, Date, Time, Result, OperationType)

Is_Seen_By (PatientCode, DoctorCode, Date, Time)

Basically i am trying to design a query that will say allow me to find the surname of the patients that have been seen by at least one of the doctors that have seen patient "P26", I am not sure on what would be the most efficient way of doing this can any1 help? thanks