const c = circuit(3);
c.x(2);    // start at position 1 = |01>

// (a) coin toss
c.h(0);

// (b) conditional shift
// decrement when coin = |0>
c.x(0);
c.cx(0, 2);
c.ccx(0, 2, 1);
c.x(0);

// increment when coin = |1>
c.ccx(0, 2, 1);
c.cx(0, 2);

c.measure();
return c;