Diode circuit with parallel voltage source
An ideal diode can only conduct in one direction,  has no forward voltage drop across it and zero resistance. Given that this is a purely theoretical circuit by defining the diodes as 'ideal' (so voltages are just voltages) I would expect this to happen:



The lowest voltage (+1V) at the cathode end of D3 would pull the diode/resistor node down to 1V. This would reverse bias D1 and D2 so they would have no effect. The voltage drop across R1 would be 4V giving a current through it of 4mA.