Final answer:
The neighbor's willingness to repair the wall in 'Mending Wall' by Robert Frost is indicated by joining the speaker to 'walk the line and set the wall between us once again' and his belief in the saying 'Good fences make good neighbours.'
Step-by-step explanation:
The lines from Robert Frost's poem Mending Wall that indicate the neighbor is willing to participate in mending the wall are:
"...I let my neighbour know beyond the hill;
And on a day we meet to walk the line
And set the wall between us once again."
These lines imply the neighbor's readiness to engage in repairing the wall. Additionally, the line:
"He is all pine and I am apple orchard.
My apple trees will never get across
And eat the cones under his pines, I tell him.
He only says, 'Good fences make good neighbours.'"
suggests the neighbor not only participates but also believes in the importance of maintaining the wall, as reflected in his adherence to the saying 'Good fences make good neighbours.'