The Indian Constitution's amendment procedure, enshrined primarily in Article 368, is indeed unique, striking a balance between rigidity and flexibility. It avoids the extreme rigidity of some federal constitutions (like the USA) and the extreme flexibility of unitary ones (like the UK), making it 'not rigid yet difficult'.

Uniqueness and Flexibility (Not Rigid):

1. Three Types of Amendment Procedures: The Indian Constitution does not prescribe a single, uniform procedure for amendment. Instead, it provides for three distinct methods, reflecting its flexible nature:
   • By Simple Majority of Parliament: Many provisions can be amended by a simple majority of both Houses of Parliament (i.e., more than 50% of members present and voting). These include matters like the creation of new states, alteration of state boundaries, abolition or creation of legislative councils in states, citizenship, and quorum in Parliament. These amendments are not considered amendments under Article 368.
   • By Special Majority of Parliament: Most provisions of the Constitution can be amended by a special majority, which requires a majority of the total membership of each House and a majority of not less than two-thirds of the members present and voting in each House. This applies to Fundamental Rights, Directive Principles of State Policy, and other provisions not covered by the first and third categories.
   • By Special Majority of Parliament and Ratification by States: For provisions affecting the federal structure of the Constitution, a more stringent procedure is required. This involves a special majority in both Houses of Parliament, followed by ratification by the legislatures of not less than one-half of the States by a simple majority. This applies to provisions like the election of the President, the extent of the executive power of the Union and States, the Supreme Court and High Courts, the distribution of legislative powers, and Article 368 itself.

This multi-tiered approach allows for easier amendment of less fundamental provisions while safeguarding the core structure, demonstrating its 'not rigid' aspect compared to constitutions that require a super-majority for almost all changes.

Difficulty (Yet Difficult):

1. Requirement of Special Majorities: The need for a special majority (absolute majority + 2/3rd present and voting) for most amendments, and further state ratification for federal provisions, makes the process inherently difficult. It requires broad consensus and often bipartisan support, preventing hasty or politically motivated changes.
2. Federal Provisions Safeguard: The requirement of state ratification for amendments affecting the federal structure ensures that the states, as constituent units, have a say in changes that impact their powers and autonomy. This acts as a significant check on the central government's power to unilaterally alter the federal balance.
3. Basic Structure Doctrine: The Supreme Court, in the landmark Kesavananda Bharati case (1973), propounded the 'Basic Structure Doctrine'. This doctrine holds that Parliament, under Article 368, cannot amend those provisions which form the 'basic structure' of the Constitution (e.g., supremacy of the Constitution, secularism, federal character, judicial review, fundamental rights). This unwritten limitation, evolved through judicial interpretation, adds another layer of difficulty and safeguard against arbitrary amendments, ensuring the enduring values of the Constitution.

In conclusion, the Indian Constitution's amendment procedure is a sophisticated mechanism that balances the need for adaptability with the imperative of preserving its fundamental principles. It is flexible enough to allow for necessary changes in response to evolving societal needs but sufficiently difficult to prevent easy manipulation or erosion of its core values.