I cannot test at this moment, but many thanks for your answer already!
How does Eviews understand that c Y1 X3 is a function of X2?
And what if X1 is also a function of Y1?
So we have:
Y1 = c + X1 + X2
X2 = c + Y1 + X3
X1 = c + Y1 + X4
How is this possible to enter into the instrument field?
X2 x Y1 X3 X1 c Y1 X4 will probably not work.
Help is appreciated